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How do you determine that the performance of your Linux server is I/O bound and, perhaps more importantly, what process or processes are casuing the problem?

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up vote 6 down vote

Top has a field called "iowait". If your system is seeing a lot of that, you know something's up. There's also iotop!

Package: iotop:
Description: simple top-like I/O monitor
 iotop does for I/O usage what top(1) does for CPU usage. It watches I/O
 usage information output by the Linux kernel (requires 2.6.20 or later)
 and displays a table of current I/O usage by processes on the system.
 Handy for answering the question "Why is my disk churning so much?".
Homepage: http://guichaz.free.fr/iotop/
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up vote 3 down vote

I wrote a comprehensive guide to tracking down performance bottlenecks on Linux systems for work: http://forms.anchor.com.au/hosting/development/HuntingThePerformanceWumpus . Covers more than you asked for, but it'll (hopefully) help you track down the problem you're seeing regardless of the actual source.

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A wall of text! – jldugger May 2 '09 at 1:07
Yeah, it's a bit wordy, I'm sure plenty of people have gone "TL;DR" at it. I prefer to give people the tools to solve problems generally rather than give pat answers to specific instances of problems, which leaves them dependent. This stuff is Hard, though, and if tracking down a performance problem isn't what you want to spend your time doing, well, you can always hire someone who's already read the article... <grin> – womble May 2 '09 at 2:34
The link is down – Jon Mar 7 at 11:47
@Jon: Sorry about that, the website was redeveloped a while ago. Link fixed. As an aside, did you downvote because a link on an answer I wrote 3 years ago broke? Talk about high standards... – womble Mar 7 at 20:03
@womble: Yes, I'm sure you'd agree that an answer which is just a non-working link is pretty useless. It doesn't really matter to the reader that it's down because it's 3 years old. Since you've fixed it, I've upvoted. – Jon Mar 15 at 0:14
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up vote 0 down vote

IoTop is probably what you're looking for.

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